WMOD00277

• Contract/Permit #: 14-06-D-6467
• Title: An Operational Adaptation Program for the Colorado River Basin
• Prepared By: Lewis O. Grant, Chappell, Crow, Mielke Jr., Rasmussen, Shobe, Stockwell, Wykstra
• Date: 10/1/1969
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

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snowfall than at Climax, however.
Despite this, it can be seen that for
Silverton (Curve A, Figure 27), for
example, some 40% of the total snow-
fall still occurs at intensities of
.02 inch per hour or less, 67% at
.04 inch per hour or less, and some
900/0 at .08 inch per hour or less.
The contribution of the higher snowfall
intensities is more apparent at the
upwind and lower elevation precipita-
tion stations in the San Juans.
Figure 28 shows, for example, at
Durango (Curve A) that only 26% of
the snowfall occurs at intensities of
.02 inch per hour or less, less than
half (46%) occurs at intensities. 04
inch per hour or less, and that only
780/0 of the snowfall occurs at inten-
sities of .08 inch per hour or less.
This is believed to again reflect the
greater percentage of precipitation at
these stations resulting from general
storm conditions in contrast to that
from orographic influences. Durango
and Mesa Verde are on the south and
southwest side of the San Juan Moun-
tains, while Ouray represents a lower
elevation station on the north side of
the range. It can be noted that the
contribution of the higher snowfall
rates at Ouray is less than at Durango
or Mesa Verde, but still greater than
at the higher mountain stations of
Silverton and Telluride.

A, Saverton, 2NE
B, Telluride
C. Wagon Wheel Gap, 3N

o .04 .08 .12 .16 .20 .24 .28 ,32 ,36 :40
INTENSITY OF PRECIPITATION

Figure 27. --Cumulative contribution of precipitation
intensities to total snowfall, November through April
1948-68.

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A, Durango
B, Mesa Ver de
C, Ouray

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INTENSITY OF PRECIPITATION

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Figure 28. --Cumulative contribut~on of precipitation
intensities to total snowfall, November through April
1948-1968. .,

42

In summary of this sub-section, it
is clear that many hours of precipita-
tion falling at low; rates accumulate
to form the snowpack in the Colorado
mountain areas. 'Hourly intensities
in the San Juan Mountains are some-
what higher than those experienced
in the northern portions of the
Colorado River B'asin; and the hourly
intensities at the 'lower elevations,
particularly those south of the San
Juans, are highest. These stations
are not reflecting the many hours of
precipitation resulting from purely
orograrb ic influences.

(2) Diurnal variation of hourly precipita-
tion
Knowledge of the diurnal variation
of precipitation is essential for
formulating appropriate program
design and program operations. This
is particularly apparent in the north
portion of the Colorado River Basin
where the diurnal variation of precip-
itation is very st].bstantial.
Distribution of snowfall with respect
to the time of day and according to
hourly intensities are shown in
Figure 29 for three winter seasons
(1964-67) at Climax, Colorado. It
can be seen from Curve A that a